Process for separating sodium chlorid from liquors containing it and sodium nitrate in solution.



l. B. HOBSBAWM & l. L. GRIGIONL' PROCESS FOR SEPARATING SODIUM CHLORID FROM LIQUORS CONTAINING IT AND SODIUM NITRATE IN SOLUTION. APPLICATION FILED MAY 2 0, 1915.

1,230, 1 62, I Patented June 19, 1917.

Inventors. Isidore B.Hobsba.wm James L.Grigion'i WMWkW Afly's a To all whom it may concern: Be it known that we, Ismonn BERKWOQD -HOBSBAWM, a subject of the King. of Great I Britain and Ireland, residing in London,

ISJJJOBE nnnxwoon nonssnwm, or

LONDON, AN ENGLAND. Z

n JAMES L. earerom, or RICHMOND,

J r nocnss'ron. snrnnarrme-somum cnnonrn' rnom motions coiv'mmme IT AND SODIUM NITLRATE IN SOLUTION.

England, and JAMES LouIs Gmerom, a sub-. ject of the King of Great Britain and Ireland, residing-in Richmond, Surrey, England, have invented a new and us'efulImproved Process for Separating Sodium,

Ghlorid from Liquors Containing It and Sodium Nitrate in Solution, of which the J so following is a specification.

This invention has reference to an- 1mproved process for separating sodium chlorid from liquors containing it and sodium nitratein solution, and an apparatus therefor.

Theliquor's or solutions which we have -more particularly in mind are those ob-' tained by the action of water on caliches, costras or any other form of naturally occurring sodium nitrate and sodium chlorid containing substances as well as the ripios or refuse dumpings from old or present nitrate workings.

In the present state of. development of the at all on the ultimate chemical composition of the liquor.'

For this reason the chlorid re'- mainin in solution becomes avariable quantity. e'liquorswith the salt in suspension are'subsequently run off'into settling tanks wherein the bulk of the sodium chlorid is allowed to'settle' to the bottom by the dual agency of gravityand'the cooling of the liquor.vv The supernatant-liquor is then decanted off into crystallization tanks which by further cooling of thefliquor the sodium nitrate is or stallized.

Such a method 0 dealing with the liquor Specification of Letters Patent.

Patented June 195, 1917.

, TApplication filed May 20,1915; eria11l'o.29,443'.

is altogether unsatisfactory for the following among other reasons (1) The supernatant liquor which is run off into the crystallizationtanks usually contains a fairly considerable and always indefinite percentage of the sodium chlorid in solution.

(2) Owing to the slowness of the deposition" of the sodium chlorid in the settling tanks and further also owing to the fact that 65 tanks is substantially reduced, an unduly the temperature of the liquor while in said large percentage of the nitrate of soda crystalizes and settles with the sodium chlorid; an p (3) The process is not continuous. It has also been known for many years T mam orrroag that by merely boiling a liquor containing Q sodium nitrate and sodiumchlorid some of the latter will be precipitated'.. The difficulty however which has existed was how to efl'ect the precipitation andseparation of all the sodium chlorid by-boiling the liquor without at the same time causing the deposition of sodium nitrate. I

The main objects ofour invention are ('1) to effect the separation of substantially the whole of the sodium chlorid from the liquor;

(2) to obtain the sodium chlorid practically free from sodium nitrate;'and (3) to effect the removal of the sodium chlorid without any fall in temperature of the liquor.

We have found that by concentrating a liquor. containingpure sodium nitrate and pure sodium chlorid in solutionup to such a point that the temperature registered at lbs. absolute per square inch, is: 123 C. practically the whole of the sodium chlorid has been rendered insoluble without incurring the deposition of sodium nitrate.

This boiling point naturally varies. according to the influence of other salts in the solution but in a pure solution of the two .abovementioned salts irrespective of the quantities of either to begin with,-this defi-' nitetemperature at which the insolubiliz'ation of the one (sodium chlorid) is complete we have designated the critical temperature.

For the attainment therefore of the said objects our process consists in raising the temperature of and concentratin liquor containing both sodium nitratean sodium chlorid in solution, until the concentration 90 normal pressure 5. e. at a pressure of 14.7

' has been carried to such a degree that the boiling'point of the liquor at normal or atmospheric pressure 2'. e. at a pressure of 14.7 lbs. absolute per. square inch is about 123 or 124 C. (more or less) and then main- I taining the concentrated liquor at that temperature. At this temperature and pres sure it will be found that sodium chlorid is 4 rendered practically insoluble in a nitrate containing solution, and the liquor must be maintained at .this temperature while' the sodium chlorid is settling. The sodium chlorid is. then removed by any suitable means fromthe desalted liquor or alternatively the desalted nitrate containing liquor may be removed, say. through a filter. The

sodium chlorid is then washed with hot water or "steam to remove the nitrate containing liquor adhering to it.

The actual temperature to which any par- 1 ticular liquorshould be raised in order to when carrying on our experimentsthe :hquor being at normal or atmospheric pressure z. c. 14.7 lbs;- absolute per square inchthat with one type of liquor the critical temperature was 122 C. and withanother 120 C. this variationas already mentioned being caused by the presence of soluble salts other than sodium chlorid and'sodium nitrate. The critical temperature of any particular liquor is determined experimentally on a sample of the liquor about to be treated on a commercial scale.

Such a test is easily and quickly performed the usual manner that is to say The chemist determines the maximum boiling point at a pressure of 14.7 lbs. per.

sqltlare inch on a sample of the liquor and 2. er freeing'said liquor from the solids which have been deposited during the concentratiom determines the absolute boiling point afresh and this is the critical tem perature.

' When the process is carried out at altitudes above'sea level, in order to attain the critical temperature the apparatus is arranged to work at a back pressure sufiicient to raise the 1 square inch.-

pressure to 14.7 lbs. absolute per Care, must be exercised that when the j liquorhas been raised to the critical temperature it shall be maintained at that tem-.

perature for a time sufficient to..allow the sodium chlorid to settle. If'the liquor how ever-is'not raised in temperature to the criti- T cal point some of the sodium chlorid will be 7 lost as it will remain in solution.

By means of our improved process above described the use of settling\tanks hereto- .fore essential, where evaporation is used, is

in the laboratory in obviated and, further, inasmuch as the so- 'dium chlorid is by our process recovered while the liquor is still at its maximum temperature the nitrate impurity in the salt is no more than that contained in the liquor naturally adhering to the crystals, and this may be subsequently removed from the salt by washing.

Our i proved process may be carried out intermi tently, that is to say, when one charge or volume of liquor has been treated as described,'the vessel wherein the concentration and desalting were effected will "be completely emptied and a fresh charge put in for treatment ina similar manner. It is however of considerable practical advan-' In said drawing the numeral'l .indicates.

the calandria of an evaporatorand' 2 a separator which is in connectionwith the calandria by'pipes 3 and 4. The liquor is conveyed to the evaporator from a suitable source by a pipe 5 having a valve 6 by which the flow of liquor may be regulated or shut completely 'ofi. At thebottom of the separator is a filter box 7 having a filtering medium 8for example wire gauze a valve 9 enabling the filter box to be put into communication withthe separator. 10

is a discharge pipe having a valve 11. The

filter box is provided with a door 12 through which access may be had to dium chlorid therefrom.

A charge of liquor to be treated, having remove the so.

been introduced tlirough the pipe 5, is heated to its boiling point in the known manner by admitting live steam through the pipe 13. The liquor circulates in the direction of the arrows 14 and the vapor given off may, if desired, be allowed to escape from the top of the separator to the atmosphere. The liquor is maintainedfat boiling point untilowing to the degree of concentration. attainedits temperature is raised to 123 or 124 C. (more orless) which is the critical temperature at which substantially the whole of the sodium chlorid will have been rendered insoluble at a pressure of about 15 lbs. absolute per square inch.

When this critical temperature has been reached and the bulk of the sodium chlorid having settled, the attendant opens the valve 9 and allows a portion of the contents from the separator to flow or dropinto the filter box 7 which is steam jacketed. The valve 9 is again closed and the valve llopened to permit the liquor from the filter chamber to flow off. This liquor is desalted nitrate containing liquor which may be run into crystallization tanks or otherwisetreated in any known manner to recover from it the sodium nitrate. The crystallized -sodium chlorid which is retained in the filter box .5 by the filter medium 8 is next washed, for

. example by admitting steam or hot-water to the upper part of the filter boxsay through a pipe 20-and thereafter the door 12 is .opened and the sodium chlorid reoved. The'hot water or condensed steam' u ed for'washing the sodium chlorid may be transferred to storagetanks.

When the door 1271s again closed it will probably'be possible to at once again open 15 the valve 9 for a further discharge from the separator 2 into the filter box and a repetition' of, the operations described.

.;---Isupply of steam that theliquor is maintained at the critical temperature notwith' standing that the volume of liquor in the evaporaor is not constant. I

The separator 2 is provided'with an apron or shield 17 which will insure that the liquor SIS-'entering-the separator through the'pipe 3,

in its circulation through the separator, shall not pass directly back to the cal'andria 1'by the'pipe 4 but shall. first travel some distance down" so as to permit the deposition 40 therefrom of the sodium chlorid held in suspension.

It islin practicepreferable to heat the [incoming liquor to someextent and for'that purpose we provide a preliminary heater 18 whichmay be connected'upwith a live steam supply but for the sake of economy is" preferably heated by the'hot' vapors from the separator- 2 the said vapor I passing I through a pipe 21. v Further, it will be obvious that instead of e live steam inlet pipe 13 has-a valve a single evaporator we may employ a multiple elfe'ct evaporator this depending on the quantity of the water to be removed from I the liquor to complete its concentratlon.

What we claim as our invention and desire to secure by Letters Patent is 1. An evaporation process for separating sodium chlorid from liquors containing it and sodium nitrate in solution, consisting in I concentrating and raising the temperature of the liquor to the point at which sodium chlorid is insoluble in the nitrate solution.

and maintaining the liquor at such tempera ture while the sodium chlorid is settling, which latter is then removed sand washed.

2. An evaporation process for separating sodium chlorid from liquors containing it and sodium nitrate in solution, consisting in concentratingand raising the temperature of the liquor to the point at which sodium chlorid .is insoluble in the nitrate solution and maintaining the liquor at such temperaofl the hot nitrate con- I reducing its temperature.

' ture while the sodium chlorid is settling and thereafter filtering taining liquor wlthout 3. A continuous process for desalting liquor containing sodium chlorid and sodium nitrate in solution, consistingv in providing a constant flow of the liquor to be desalted to an'evaporator at'a rate faster than that at. which the evaporation therem is being eflectedwhile maintaining the temperature of the liquor at a point at which sodium chlorid is insoluble'in the solutionso that a constant deposition of the sodlum chlorid takes place and an average level of the liquor is maintained notwithstanding intermittent removal from the evaporator of the deposited sodium chlorid and of, de-

salted liquor.

In testimony whereof we have signed our names tothis specification inthe presence of two subscribing witnesses; I

I I. BERKWOOD HOBSBAWM.

J. L. GRIGIONI.

Witnesses:

' A. E. WILLIAMs, POLLON. 

